Method for marking an indication to the lens

ABSTRACT

Plastic eyeglass lenses and the like are marked with an identifying character or symbol by applying to the surface thereof or dissolving or comelting therein a flourescent dyestuff according to the disclosed method. When the proper amount of flourescent dyestuff is included the lens appears normal in sunlight but is characteristically marked in whole or in part under ultraviolet light depending on the area treated.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method for marking an indication on plasticlenses for eye-glasses.

2. Description of the Prior Art

The plastic lenses (hereinafter referred to only as lenses) are made ofpolymethylmethacrylate, polystyrene, polycarbonate, cellulose-acetate,diethylene glycol bis allyl carbonate, referred to hereinafter as CR-39,etc., and those lenses are widely used because of their excellentcharacteristics, such as light weight, shock resistance, heat resistanceand solvent resistance.

In the prior art for marking such lenses, there are methods such asprinting an indication on the lenses. However, such methods provide anunacceptable appearance, engraving on the lenses, high cost, the longtime required to apply such works, easy peel-off of the printedindication and damage the lenses.

The present inventors have been making efforts to solve such drawbacksand to provide an easy method for marking the indication on such aplastic lens which is noticeable first when exposed to ultraviolet rays.

SUMMARY OF THE INVENTION

This invention provides various methods for providing a marking on aplastic lens characterized in that a whole or part of the lenses isprovided with fluorescent dye suitable methods comprise steps of mixingfluorescent dye with the melt of materials for making the lenses, andforming them into lenses and then dying a whole or part part of suchlenses with the melt of the dye stuff.

One aspect of this invention is such that the melt of the materials forlenses and the fluorscent dye stuff melt together and are formed in ashape of the desired lenses.

Another aspect of the invention is that the whole or only part of thelenses are dyed and colored with fluorescent dye stuff.

Still a further aspect of this invention is such that the plastic lensesmay be conveniently printed with ink which contains the flourescent dyemelted in alkohol, etc.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

FIG. 1 is a transmission rate curve of the ultraviolet portion and thevisible portion of CR 39 lenses according to the invention and the CR-39lenses containing no fluorescent dye; and

FIGS. 2a and 2b are, respectively, perspective views showing thecondition of the lenses printed with indication according to Example 4under sunlight and the condition when the ultraviolet rays are appliedthereon.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the preferred embodiments according to this invention will behereinafter discussed with reference to the accompanying drawings.

The first method is characterized in that to the material for the lensor materials therefor is added 0.01%-0.00001 weight % of a fluorescentdye (hereinafter weight %), and preferably 0.001-0.0001% and thedyestuff plus plastic are homogeneously melted together and then formedinto a lens according to the conventional method.

Fluorescent dye may be any kind of the type which melts homogeneouslywith the lens materials. However, if the concentration of thefluorescent dye is above 0.01%, it is not preferable in a lens since itemits sunlight or fluorescent rays inside a room. The lenses treatedwith the fluorescent dye at less than 0.00001% concentration do not emitfluorescent rays which are seen by the human eye even when theultraviolet rays are applied thereto and such lenses are accordingly notpreferable. According to the density or concentration used in thisinvention, the lenses are as same as the normal conventional lenses whenthe sun rays or the room rays strike the lenses but upon application ofultraviolet rays i.e. black light, etc., the lenses emit fluorescentrays which are easily distinguished by the human eyes.

Then, the second method of dying the lenses with the fluorescent dye ischaracterized in that the fluorescent dye is dissolved or melted inwater as seen in the conventional dyeing method for the lenses ordispersed therein, and the lenses are soaked and immersed within thedyeing solution and thereby dyed. However, the lenses do not emitfluorescent rays when exposed to ultraviolet rays, but when the densityof the fluorscent dye is within a range of 0.00001%-0.0000% the lensesemit fluorescent rays.

The addition of a surface active agent as the dispersion agent ispreferable. Although the solution temperature is appropriate at 60-95°C., we have found that 70° C. is the best for the polymethylmethacrylateand 80° C. for CR-39 lenses, taking into a consideration the evaporationof the solution, operation, and the influence of the lenses. The normaldying time is about 10 seconds to 30 minutes which time is convenientlyselected according to the dye density, temperature of the solution andthe materials, so as to fulfill the objects of the invention.

There are two ways of dyeing, one being dyeing all the lenses, anotherbeing a partial dyeing of indication of only the symbols or letters. Inthe former the lenses are immersed in the dye solution and finishedlenses provide the same effect as when the dye is melted and mixed withthe lens materials. The latter lenses are provided with a convenientmask for the symbols or letters which are in turn dyed. This method isconvenient when the manufacturers affix the diopter, as in the case ofcorrective lenses, or manufacturers' numbers for reference.

Furthermore, the method of printing the indication on the lensesprovides a same effect as the dying method of the symbol or letters,etc. The prior art printing of the indication employs a printing by anon-aqueous soluble ink, which requires that the ink be projected by acertain thickness and that it is easily solved or melted by an organicsolvent. To the contrary, in our invention, the printed indication isnot protruded on the lens surface, it is not soluble by the organicsolvent and it is semi-perpetually printed and discriminated. Suchlenses do not emit the fluorescent rays but emit the fluorscent rayswhen the ultraviolet rays are applied thereto, such function being theobjects of this invention.

The printing method of this invention is explained hereinafter. Thefluorescent dye is dissolved in alcohol and the ink is adjusted. A0.05-10% concentration of the fluorescent dye in this solution ispreferable and it is selected so as to be melted completely. An alcoholsuch as methanol, ethanol, isopropanyl, benzyl alcohol, etc., is usablebut among which, the isopropanol is the best in the light of thesolvency of the dye and evaporation rate of the solvent, etc. Theaddition of about 10% glycerine in the alcohol is preferable since itsuppresses the evaporation rate of the alcohol. Any material other thanalcohol is usable so long as it dissolves the fluorescent dye and itdoes not affect the lens. The adjusted fluorescent ink as describedabove is preferably adsorbed onto a rubber stamp which is in turnpressed onto a lens surface. Only such pressing is required to apply theink onto the lens and the lens is then placed inside a dryer at 60°-90°C., preferably 80° C. for 10 minutes whereby the ink is caused to betransmitted into the lens interior. Thus the printed lens appears to bethe same as the convention lens under sunlight but upon application ofthe ultraviolet rays the symbols or letters thereon can be read. Evenwhen the lens surface is wiped by water or an organic solvent (except,of course, those that dissolve lens per se), the printed symbols orletters are not removed.

Now, the examples according to this invention will be discussed. Unlessotherwise indicated all parts and percentages are by weight.

EXAMPLE 1

A material of allyl diglycol carbonate (CR-39) for a plastic eyeglasseslens has added thereto diisoproperoxidicarbonate, Chinubin-P (sold byCiba-Geigy) as the ultraviolet ray absorption agent and 0.001%fluorescent dye stuff (White flour B sold by sumitomo Chemical Co.) ishomogeneously melted and then the lens is formed according to theconventional manner. The thus formed lens is the same as the normal lensunder sunlight but upon application of black-light the whole lens emitsfluorescent rays, which are visible by human eyes.

The ray transmission rate curve of the ultraviolet portion and thevisible portion of the normal lens of CR-39 lens in the same shape asthe lens containing no fluorescent rays vs. the lens according to thisExample 1 was plotted and there is found no difference by addition ofthe fluorescent dye.

EXAMPLE 2

Five mg of a fluorescent dye stuff (White flour B or White Flour PCSsold by Sumitomo Chemical Co.) is poured into 1 liter of water and asmall amount of Toho salt A-10 as a surfactant (sold by Toho ChemicalCo.) is then added. The mixed water is then agitated and kept at 80° C.The lens made of CR-39 is immersed and soaked within said dye solution,washed with water and then wiped for 5 minutes with acetone. The thustreated lens is the same as the normal lens under sunlight but uponexposure to black light, it emits the fluorescent rays which are visibleby human eyes.

EXAMPLE 3

A lens made of polymethacrylate is dyed in the same manner as in Example2 and the same result is obtained. However, acetone is not used.

EXAMPLE 4

Two hundred mg of a fluorscent dye stuff (White flour B or White flourHCS sold by Sumitomo Chemical Co.) is melted in 200 mg of isopropanoland furthermore, glycerine is added. The solution is mixedhomogeneously. This solution is absorbed into a stamp made of porousrubber and said stamp is pressed onto the lens made of CR-39 and thelens is dried in a dryer at 80° C. for 5 minutes. The thus obtained lensis cleaned with acetone and upon receipt of the black-light thereon, theletters printed on the lens as shown in FIG. 2b are visible, however,upon termination of the application of black-light the letters areinvisible as shown in FIG. 2a.

The lenses provided with an indication according to the abovementionedmethods of this invention provide a means for clearly and easilydistinguishing the lenses made by various companies. It also providesforconvenient aftercare of the lenses.

We claim:
 1. A method of marking an indication on a plastic eyeglasslens which indication is visible only in ultraviolet light, said processcomprising the steps of:(1) printing the desired symbol or letter on theplastic lens surface with a fluorescent dyestuff present to the extentof about 0.05 to about 10% by weight, said dye-stuff contained in anorganic solvent solution, and thereafter (2) drying the thus printedfluorescent dyestuff solution at about 60° to about 90° C. for 1 to 10minutes thereby causing the fluorescent dyestuff solution to betransmitted into the interior of the pastic lens.
 2. The methodaccording to claim 1 wherein the dyestuff is dissolved in an alcoholselected from the group consisting of methanol, ethanol, isopropanol andbenzyl alcohol.
 3. The method according to claim 1 or claim 2 whereinsaid solution also contains glycerine up to about 10% by weight.
 4. Themethod according to claim 1 or claim 2 wherein said solution is absorbedin a rubber stamp which prints the letter or symbol on the lens surface.